This invention relates to airfoils for gas turbine engines and more particularly to airfoils with cast-in tip caps, airfoils with impingement cooled squealer tips, bimetallic airfoils, and methods for making and repairing airfoils.
Airfoils in gas turbine engines experience durability problems at the tip of the airfoil in the form of cracking due to thermally induced stress and material loss due to oxidation. This can be addressed by using an alloy having increased resistance to environmental oxidation and corrosion. However, it is undesirable to upgrade the entire airfoil to a more thermal-resistant and oxidation-resistant alloy because this increases component cost and perhaps weight.
Bowden, Jr. et al., U.S. Pat. No. 5,794,338 discloses a blade originally manufactured with a one-piece body of a single superalloy which is removed from service after being damaged. The blade tip is repaired by removing damaged alloy material and replacing it with a different alloy more resistant to environmental oxidation.
Lee et al., U.S. Pat. No. 5,348,446 discloses an airfoil having a core body of a first alloy and a U-shaped blade tip of a second alloy bonded to a flat roof of the core body.
Tip wear has also been addressed by increasing cooling efficiency at the tip. Various cooling arrangements are disclosed in Lee et al. U.S. Pat. No. 5,183,385, including impingement cooling of the squealer tip via angled impingement cooling holes in a brazed-on tip cap. Dennis et al., U.S. Pat. No. 3,899,267 discloses an alternative impingement cooling arrangement. One deficiency of the prior art cooling arrangements, wherein the full length of the squealer tip is cast integrally with the tip cap and the core body, is that angle impingement cooling holes cannot be drilled into the tip cap because the full height of the squealer tip interferes with the line of sight for drilling cooling holes. This problem is further exacerbated in a design having a tip shelf, in which the tip cavity is relatively narrow in comparison to a design not having a tip shelf.
Briefly, therefore, the invention is directed to an airfoil having a one-piece core body having, upon original manufacture, an airfoil body, an integral partial height squealer tip, a tip shelf formed at the junction of the airfoil body and the partial height squealer tip, an integral tip cap between the airfoil body and the integral partial height squealer tip, and a squealer tip extension bonded to the partial height squealer tip.
The invention is also directed to an airfoil having a one-piece core body formed from a first superalloy comprising, upon original manufacture, an airfoil body and an integral tip cap. There is also a squealer tip bonded to the core upon original manufacture and having at least a portion thereof formed from a second superalloy distinct from the first superalloy. A tip shelf is formed at the junction of the airfoil body and the squealer tip. The second superalloy comprises, by approximate weight percent, 0.1 to 0.15 C, 6.0 to 7.0 Cr, 0.01 to 0.02 B, 5.5 to 6.5 Al, 2.5 to 3.5 Re, 4.5 to 5.5 W, 1 to 2 Mo, 11 to 13 Co, 6 to 7 Ta, 1 to 2 Hf, and the balance Ni.
In another aspect the invention is an airfoil comprising a one-piece core body having an airfoil body, an integral partial height squealer tip, a tip shelf formed at the junction of the airfoil body and the partial height squealer tip, and an integral tip cap between the airfoil body and the integral partial height squealer tip. There is a squealer tip extension bonded to the partial height squealer tip, cooling holes in the integral tip cap which holes are angled to direct cooling toward the squealer tip extension.
The invention is further directed to an airfoil manufactured by forming a one-piece core body comprising an airfoil body, an integral partial height squealer tip, a tip shelf formed at the junction of the airfoil body and the partial height squealer tip, and an integral tip cap between the airfoil body and the integral partial height squealer tip; by drilling a cooling hole in the tip cap which cooling hole is angled to direct cooling at the squealer tip extension; and by bonding a squealer tip extension to the partial height squealer tip.
In another aspect the invention is an airfoil of the type having an airfoil body, a tip cap, a squealer tip, and a tip shelf formed at the junction of the airfoil body and the squealer tip, which airfoil is repaired by removing at least a portion of the squealer tip, drilling an impingement cooling hole in the tip cap which cooling hole is angled so as to provide impingement cooling, and replacing the at least a portion of the squealer tip.
The invention is also a method for manufacturing a gas turbine engine airfoil of the type having an airfoil body, a tip cap having a film cooling hole therein, a squealer tip, and a tip shelf formed at the junction of the airfoil body and the squealer tip. The method is forming a one-piece core body comprising an airfoil body, an integral partial height squealer tip, and an integral tip cap between the airfoil body and the integral partial height squealer tip; and bonding a squealer tip extension to the partial height squealer tip.
The invention is additionally directed to a method for repairing a gas turbine engine airfoil of the type having an airfoil body, a tip cap, a squealer tip, and a tip shelf formed at the junction of the airfoil body and the squealer tip. The method involves removing at least a portion of the squealer tip, drilling an impingement cooling hole in the tip cap which cooling hole is angled so as to provide impingement cooling, replacing the at least a portion of the squealer tip.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.